209 
FXUS63 KLSX 020425
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1025 PM CST Mon Dec 1 2025

.KEY MESSAGES...

- Light to moderate snow is expected this evening, before exiting from
  northwest to southeast. Additional snow amounts of 1-2" are 
  expected.

- Seasonably cold temperatures will continue through the weekend,
  with another Arctic blast expected late Wednesday through
  Thursday. 


&&

.SHORT TERM...  (Through Late Tuesday Afternoon)
Issued at 227 PM CST Mon Dec 1 2025

Moderate, to occasionally heavy, snow has moved east/northeast 
over into west central and south-central Illinois and should exit 
over the next 1-2 hours. There should be a 4-6 hour window with 
lighter, spottier snow across much of the area this 
afternoon/early evening. The exception is parts of northeast 
Missouri and west-central Illinois where light to moderate snow 
should be more continuous. Another round of light to moderate snow
should move northwest to southeast this evening across the entire
area. This snow will be aided by moderately strong low/mid level 
frontogenesis and the main midlevel shortwave trough moving 
through the region. Snowfall rates should be more modest than the 
earlier round, generally in the 0.25-0.50"/hr range. 

By the time the snow ends, a max band of 3-4+" is expected across 
parts of central Missouri east/northeast into south-central Illinois 
just north of the I-70 corridor. The snow amounts taper down sharply 
once you head southeast of the I-70 corridor, as these areas saw 
much lighter snow amounts this afternoon than neighbors further 
north. For this evening's round, additional snow of 1.0-1.5" should 
be common for most of the area, with some totals as high as about 2".

The concern for Tuesday shifts to low-level clouds and temperatures. 
Guidance is showing low stratus clouds to hang on well into the day 
on Tuesday, particularly for parts of eastern Missouri over into 
west central and south-central Illinois. Given that these locations 
also have some fresh snow cover, temperatures should really struggle 
to rise that much. Highs in the mid to upper 20s are forecast for 
these areas. Further southwest, highs in the low to mid 30s are 
expected in central and southeast Missouri. Parts of central 
Missouri will have a snow pack, which could lead to slightly lower 
high temperatures than forecast. There is more confidence in 
southeast Missouri. This part of the CWA should not have as much 
snow cover and should see some sunshine.


Gosselin

&&

.LONG TERM...  (Tuesday Night through Next Monday)
Issued at 227 PM CST Mon Dec 1 2025

(Tuesday Night - Wednesday)

Moderating temperatures are forecast heading into midweek as low-
level winds turn out of the southwest ahead of an approaching cold 
front. Lows Tuesday night will still be cold however as a surface 
ridge of high pressure works eastward into the Ohio Valley. Lows in 
the mid teens to low twenties are forecast. Areas with still 
(relatively) fresh snow cover though into south-central Illinois 
still may not be cold enough. Winds shouldn't pick up until after 
0600 UTC, so we could see some single digits potentially. Highs on 
Wednesday are expected to range from the mid 30s to mid 40s from 
north to south ahead of the front. There is a bit more uncertainty 
with highs in our far northwestern counties as the front should move 
through there during the early afternoon. A slightly earlier (later) 
passage could yield highs a few degrees colder (warmer) than 
forecast.


(Wednesday Night - Thursday Night)

The arctic cold front will move through most of the CWA Wednesday 
evening. Behind that front, a brief but strong push of unseasonably 
cold air is expected. We also will have to watch for some light snow 
to occur due to low/mid level frontogenesis behind the front. LREF 
probabilities for measurable snowfall are in the 20-50% range across 
the area. From past experience, these arctic fronts are efficient at 
squeezing out some light snow. Any snow that does fall though would 
likely be efficient (high SLR) and accumulate as temperatures 
rapidly fall through the 20s. PoPs may need to be adjusted upwards 
and expanded if this signal remains or increases in the next 24 
hours.

Wednesday night's lows will vary sharply from northwest to 
southeast. Parts of northeast Missouri are expected to go below 
zero, whereas lows in southeast Missouri and southwest Illinois are 
forecast to be in the upper teens. Thursday is expected to be the 
coldest day of the young winter season so far with highs ranging 
from the mid teens to near 30 degrees from north to south. 

Timing of the surface high does not look ideal at this point for 
radiational cooling Thursday night as it quickly scoots out into the 
Ohio Valley. This should keep lows in the single digits/teens across 
the region.


(Friday - Next Monday)

Broad northwest flow aloft is expected this weekend into early next 
week. Deterministic guidance shows multiple midlevel shortwaves 
coming across the Mississippi Valley. These look like hybrid 
clippers, with accumulating snow along/poleward of their tracks. 
This far out, it is difficult to say when/where they will occur, but 
climatology heavily favors these systems mostly impacting areas to 
our north.

Temperature wise, largely below normal readings are forecast through 
the period. The uncertainty comes with the individual clippers 
themselves as they can yield higher temperatures than forecast ahead 
of the, with colder temperatures in their wake. The latest NBM shows 
the uncertainty well, with inter-quartile ranges for highs around 10 
degrees.


Gosselin

&&

.AVIATION...  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1018 PM CST Mon Dec 1 2025

Bands of snow continue to push east through east-central/southeast
MO and southern IL tonight. Within these bands, expect IFR to LIFR
visibilities. Snow is on track to exit the area completely between
09z and 12z. Low MVFR to IFR ceilings will persist well behind the
front, not clearing until Tuesday afternoon. In the meantime, a
growing number of terminals across Missouri have begun to report
freezing fog with one report of freezing drizzle. Reports have 
been few and isolated, and we expect it to remain this way. We
will continue to monitor and amend as needed.

Jaja

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...Winter Weather Advisory until midnight CST tonight for Crawford 
     MO-Franklin MO-Jefferson MO-Lincoln MO-Saint Charles MO-
     Saint Louis City MO-Saint Louis MO-Warren MO-Washington MO.

     Winter Weather Advisory until 3 AM CST Tuesday for Iron MO-
     Madison MO-Reynolds MO-Saint Francois MO-Sainte Genevieve 
     MO.

IL...Winter Weather Advisory until midnight CST tonight for Bond IL-
     Calhoun IL-Fayette IL-Greene IL-Jersey IL-Macoupin IL-
     Madison IL-Monroe IL-Montgomery IL-Saint Clair IL.

     Winter Weather Advisory until 3 AM CST Tuesday for Clinton IL-
     Marion IL-Randolph IL-Washington IL.

&&

$$

WFO LSX